Carpenter AerMet® 100 Alloy is a nominally 0.23% C, 13.4% Co, 3.1% Cr, 11.1% Ni, 1.2% Mo and balance Fe proprietary alloy designed for aerospace structural applications requiring a combination of high strength, high fracture toughness and good resistance to stress corrosion cracking. AerMet® 100 alloy was designed to be a candidate to replace 300M in the Navy's carrier based aircraft but it is now being evaluated for other applications where its nominal 285 ksi (1965 MPa) U.T.S., 115 ksi √in. (126 MPa √m) KIc and 35 ksi √in. (38 MPa √m) KIscc in a 3.5% NaCl solution can be utilized. This paper presents AerMet® 100 alloy and discusses its typical properties after the recommended 1625°F (885°C), 1h solution treatment and 900°F (482°C), 5 hour age. AerMet® 100 alloy is then compared with AF1410, Marage 250, 300M, H11, HyTuf and 4340. Finally, aging curves for AerMet® 100 alloy aged for 5 hours between 200 and 950°F (93 and 510°C) are presented and the effects of aging treatments on mechanical properties are discussed.